Step 9 & 10 - Power Tube Sockets & Switches/Fuses

[Billy Batz]

Step 9 is just like the 100W instructions. A piece of yellow wire between pin6 of all 4 tube sockets. I tend to use shorter ones like some old marshalls. Just an aesthetic preference.

Step 9b is somewhat different. The instructions have you put a 5k6 resistor on every power tube pin5. The actual 45/100 amps used 2 'swamp' resistors at 1k5 ohms for all 4 tube sockets. They went one between V4 & 5, then again one between V6 & 7. Its up to you. I chose to use the 2 but at 5k6. These amps shouldnt have as much oscillation trouble as the 69 100W kit but it is possible that Ill need to change to all 4 sockets if the amp has too much oscillation such as squealing or a squeaky warble following your notes.

When you use 2 resistors between the inner and outer sockets like that you can use some of the sleeving to insulate the bare leads.

If you use all 4 connect the resistors as shown in step 9c & 9d.

I also went ahead and attached the 4 screen-grid resistors as shown in step 9e.

I install the board standoffs/spacers earlier in the build process to help get an idea how the wires routed under the board will go and how long they need to be.

Also I sometimes with use a hot glue gun to make sure wires under the board- like the OT primary twist- will stay put.

[Billy Batz]

At step 10 I went ahead and screwed on the 2 switches. Actually I did that earlier when I was waiting for something else. I used the simpler more accurate Carling switches.

You cant do anything with the PT secondary until the power board is installed. So I left that for now and you can skip step 10b and 10c. 10d is irrelevant.

10e is similar. Solder a wire to one side of the AC switch thats long enough to go to the voltage selector- maybe with a few inches to spare. If your using one of the later style double pole switches then route it through both the bottom lugs as shown in the instructions.

10f and 10g are irrelevant.

10h is different. You can attach the single panel mounted fuse holder. The other fuse holder is flush mount. It attaches to the bottom of the chassis inside the amp. There was no screw hole on my chassis for this so I had to drill one to attach that fuse holder.

[Billy Batz]

First up is to wire up the voltage selector. The switch spaces are for 110(120), 220 & 230. Any extra voltage taps from the PT tie off or clip off and heat shrink. Each tap goes to its space on the bottom of the switch as your looking in the chassis as it does on the impedance selector. The common lug on the impedance switch gets the wire from the one lug (or bottom 2 lugs if you have the later style switch) of the AC switch. The other lug (or top 2 of the later style switch) goes to the hot (labeled-L or black wire) side of the power cord or IEC socket.

The flush mount fuse inside the chassis has no hole on the chassis. Theres one in the opposite corner on the preamp side that looks conspicuous and has no apparent purpose so it was probably a mistake. Anyway wire the PT secondary's HT CT to one end of this fuse and wire th other end to its own chassis ground tab.

The Mains fuse on the rear panel is wired just like the instructions for the 100W kit. The neutral from the power cord (N on an IEC socket) goes to one terminal on that fuse holder. The other goes to the common lug of the PT primary.

The lamp gets mounted and wired the same way. The red lead to the PT side of the AC switch- the black lead to the PT side of the mains fuse.

steps 10n through 10r are irrelevant

[gutpile]

some more pics...

[Flames1950]

As an aside, I have not found evidence of the 470ohm screen resistors being used on the 100's. Even the old hand-drawn schematics show 1K's, as do all the research pics I could scrounge up.

George, your '66 have 1K's on the screens? Or is it the one exception we can find?

OK, the alleged Dickinson "Hendrix" amp does have 470's though I question their originality.........

[Billy Batz]

I question everything different about that amp.

[Flames1950]

I question everything different about that amp.

Amen brother Billy!!!

[shakti]

I went with the two single 1.5k "swamp" resistors between the grids (pin 5) of V6/7 and V4/5 respectively, as seen on most original JTM45/100s. However, I got the advice from a respected transformer manufacturer and amp builder to put a 5.6k on each single power tube.

How does this affect the performance of the tubes and amp? Does it affect ghosting in any way? Or tube wear?

[shakti]

Anyone? Looking at the schematic, it seems this would affect the bias voltage of the outer pair of tubes. Theoretically, couldn't this lead to a less-balanced set of tubes, and thus theoretically more ghosting?

Also, I've had trouble with a loud put-put-put sound (motorboating?) with the bass turned up high (say, 6-7 or above) and the amp turned up loud. It's not a problem at lower volumes. I don't tend to set the bass that high, but could this be remedied by putting 5.6k grid stoppers on each tube?